In recent years, with respect to portable terminal devices used for mobile communication, small-size and light-weight devices have been developed, and in order to achieve devices having multiple bands required for a plurality of communication systems and portable terminal devices with multiple functions, the number of built-in circuits has been increased. For this reason, in order to improve packaging density, there have been strong demands for miniaturizing the electronic parts to be used therein into small-size parts capable of being surface-packaged.
Here, surface acoustic wave apparatuses have been used as key parts for the portable terminal apparatus. In the surface acoustic wave apparatus, it is necessary to form a hollow portion near the electrode face on which surface acoustic waves are excited so as to ensure a vibration space, and also to air-tightly seal the vibration space. For this reason, the surface acoustic wave apparatus is housed, for example, in a ceramic package. With respect to this surface acoustic wave apparatus also, there have been strong demands for a small-size surface acoustic wave apparatus capable of being surface-packaged, which is low-loss, and has a superior blocking characteristic against frequencies outside the passband.
In response to this demand for small sizes, a surface acoustic wave apparatus having a WLP (Wafer Level Package)-type surface packaging structure has been proposed (for example, see JP-A 9-172339 and Japanese Patent Application National Publication (Laid-Open) No. 2005-537661).
FIG. 9 is a view describing a conventional method for manufacturing a surface acoustic wave apparatus. In the conventional method for manufacturing a surface acoustic wave apparatus, first, as shown in FIG. 9(a), a sacrifice layer 963, made from polysilicon, amorphous silicon or the like, is formed so as to cover a surface of an electrode pattern 962 of a surface acoustic wave element formed on a piezoelectric substrate 961, with at least one portion of an electrode pad 968 connected to the electrode pattern 962 being exposed. Next, as shown in FIG. 9(b), after a protective cover 964 has been formed so as to cover the sacrifice layer 963, a through hole 965 is formed through the protective cover 964 so as to allow the inner sacrifice layer 963 to be exposed. Next, as shown in FIG. 9(c), the sacrifice layer 963 is removed through the through hole 965, by using a dry etching method or the like, so that a hollow portion 966 is formed above the electrode pattern 962; thus, a surface acoustic wave apparatus is obtained.
However, as shown in FIG. 9, in the case where the protective cover 964 is formed by using the sacrifice layer 963, a problem arises upon removing the sacrifice layer 963 in which electric characteristics of the surface acoustic wave apparatus deteriorate due to etchant and etching products remaining in the hollow portion 966.
Moreover, many processes are required in the manufacturing process for forming the hollow portion 966, resulting in a problem of complex manufacturing processes.